This invention relates to a coaxial connector for terminating to a high performance coaxial cable of the type that has a wrapped conductive shield. A coaxial cable includes a solid or stranded inner cable conductor surrounded by a layer of polymer dielectric material. The dielectric material is precisely centered within a woven braid outer cable conductor, and the cable has an outer jacket of polymer material. The outer cable conductor defines a ground return path which is necessary for microwave signal transmission.
High performance, low loss coaxial cables have been developed to transmit higher frequencies with minimal impedance discontinuities. With low loss dielectrics, these cables may transmit higher power levels with minimal attenuation. The high performance cables generally comprise an inner cable conductor surrounded by a low loss dielectric material such as cellular polyethylene, a thin wrapped metallic outer shield such as a conductive foil, a woven plated copper braid shield, and a polymer outer jacket such as polyvinyl chloride (PVC). This type of cable is desirable for use in the transmission of high rate digital signals such as those used in the High Definition Television (HDTV) industry, of a frequency of about 1 GHz and higher. FIG. 1 shows such a high performance coaxial cable 1 which comprises a center cable conductor 3 and an outer cable conductor 7 formed by a thin wrapped metallic foil 7a and a woven braid outer conductor 7b. A dielectric material, or insulator 5 separates the center conductor 3 and the outer conductor 7. The entire cable 1 is enclosed in an outer jacket 9.
Cables are generally prepared for termination to a coaxial connector by stripping, or removing, from around the center cable conductor, the dielectric material, the braid and the cable jacket to strip lengths specified by the manufacture of the RF coaxial connector. In the case of the high performance coaxial cable having a wrapped metallic foil shield, the foil is generally removed and stripped back approximately evenly with the jacket, as shown in FIG. 2a. The removal of the metallic foil in this way is an inconvenience for cable assembly manufacturers and cable installers because it requires the foil to be stripped back behind (within) the braid that surrounds it. This operation is time consuming and requires special tools, and may lead to damage of the braid.
A preferred termination technique would be to leave the metallic foil intact, i.e. flush with the dielectric material and/or braid. However, this presents a problem in terms of electrical performance. At lower frequencies, cables prepared and terminated in this way exhibit no electrical performance problems, with particular respect to return loss. However, at higher frequencies, a convoluted signal path occurs, and a higher than expected return loss or VSWR (voltage standing wave ratio) is exhibited.